Sudan’s government on Sunday confirmed it had moved troops to a volatile energy-rich central region, telling state media it wanted to halt "feverish attempts" to attack the area by Darfur rebels. The deployment into South Kordofan raised tension in the province that contains key oil fields and borders some of Sudan’s most sensitive areas, including Darfur.

Sudan said it had built up its forces "to thwart the feverish attempts of JEM to transfer their activities to the state of Southern Kordofan".

The announcement came days after officials in semi-autonomous southern Sudan accused the north of building up a large force in South Kordofan over the past three weeks.

A southern official on Friday said the new deployment of six northern battalions broke the terms of the constitution and the 2005 peace deal that ended two decades of north-south civil war.

On Sunday, an unnamed government spokesman told the state Suna news agency the northern army had built up its forces "to thwart the feverish attempts of JEM (the Darfur rebel Justice and Equality Movement) to transfer their activities to the state of Southern Kordofan“.

There have been unconfirmed rumours circulating among United Nations agencies, aid groups and government bodies that a JEM force crossed into South Kordofan around three weeks ago.

No one was immediately available to comment from JEM, a movement which has fought in South Kordofan before and repeatedly said it wants to take its struggle beyond Darfur to what it sees as other marginalised areas of Sudan.

The rebel movement’s spokesman last week told Reuters he would not "confirm or deny“ a new JEM push into South Kordofan.

The Sudanese government has been on the lookout for large-scale movements of JEM forces since the insurgents launched an unprecedented attack on the country’s capital Khartoum in May.

The government told Suna on Sunday it had sent assurances that the new northern forces had no intention of attacking the south’s Sudan People’s Liberation Army also deployed in the area.

The statement did not respond to the southern accusations that the move broke the terms of the 2005 peace deal.

The north and the south have had a troubled relationship since the signing of the Comprehensive Peace Agreement. Their troops have clashed, most recently in May over the oil town of Abyei, which both sides claim.

Under the deal, the north’s Sudan Armed Forces were to be reduced to pre-war levels in South Kordofan, one of three "transitional areas“ bordering the south where large sections of the population supported the southern rebels during the war.

The International Crisis Group think tank said in October the 2005 peace deal was at risk in South Kordofan, which had "many of the same ingredients“ that produced the raging conflict in the neighbouring region of Darfur.

Sudan says it produces 500,000 barrels of oil a day, a figure which it hopes to raise to 600,000 in 2009.